ON THE AXIAL BEHAVIOR OF HIGH STRENGTH CONCRETE COLUMNS CONSIDERING FIRE SAFETY

Transverse steel reinforcement confinement in reinforced concrete columns is mainly required to provide ductile behavior, minimum core capacity, and prevention of longitudinal bar buckling. The common passive confinement by transverse steel rebar action is less effective in high-strength concrete (HSC) than in normal-strength concrete. Therefore, the transverse steel amount required by the standards for HSC columns is high, and in some cases, particularly in the lower stories of high-rise buildings, their implementation is impractical. A possible solution is the application of FRP-wrapping/tube confinement, as suggested in previous research studies, but the low fire resistance of the polymer impairs the fire resistance of the columns. A new construction method using textile-reinforced concrete as internal confinement together with reduced transverse steel reinforcement is presented. Fire safety is considered by eliminating the FRP vulnerability to high temperatures. This is enabled by attaching the FRP to the conventional reinforcement, thus protecting it by the concrete cover. Initial experimental results of the first phase of the research, which aims to deal with the behavior under ambient conditions, are presented. The tests were planned based on predictions from an adapted model that was originally developed for externally applied FRP reinforcement. Analysis of the uniaxial load-displacement behavior of circular columns is performed by comparing different amounts of conventional steel and carbon fibers to examine each component influence. The results give an insight into the effectiveness of the proposed method for construction.